This invention relates to a diagnostic device in which data representative of the conditions of various parts of the charging system of a vehicle are inputted with a predetermined period (sampling frequency), so as to monitor the operating conditions of the various parts, to diagnose whether these parts are normal and to display the results of such diagnosis.
A charging system of this type is arranged as shown in FIG. 1. In FIG. 1, reference numeral 1 designates a generator having an armature 1a and a field coil 1b; 2, a rectifier for rectifying the output of the generator 1, i.e., the three-phase AC outputs of the armature 1a; 3, a voltage regulator for regulating the generated voltage of the generator 1, the voltage regulator 3 having a voltage detecting terminal a, a terminal b connected to the field coil 1b, for allowing a controlled field current, a grounding terminal c which also supplies a current for initially exciting the generator 1; 4, an ordinary battery containing electrolyte; 5, a key switch which is closed to start the internal combustion engine (not shown); and 6, a pilot lamp connected between the terminals a and d, the pilot lamp 6 being turned on or off according to the difference between the voltages at the terminals a and d. The voltage regulator comprises diodes 306 and 314; transistors 307 and 308; resistors 309, 311, 312 and 313; a comparator 310 and a reference voltage source 315.
When the key switch 5 is turned on, a starter (not shown) starts the internal combustion engine, so that the armature 1a of the generator 1 is rotated. While the speed of the armature 1a is low, the initial field current flows from the battery 4 through the key switch 5, the terminal d of the voltage regulator 3, the diode 314, the resistor 313, the terminal a, the field coil 1b, the terminal b, the transistor 307 and the terminal c to ground, so that the pilot lamp 6 is turned on by the difference between the voltage at the terminals a and d. As the speed of the armature 1a increases, the generated voltage of the armature 1a is increased and the voltage at the terminal a is increased, so that the difference between the voltages at the terminals a and d is decreased and accordingly the pilot lamp 6 is turned off. As the voltage at the terminal a is increased, the voltage at one input terminal of the comparator 310, which is determined by the voltage division ratio of the resistors 311 and 312, is also increased. When this voltage exceeds the reference voltage provided by the reference voltage source 315, the state of the output of the comparator 310 is changed. As a result, the transistor 307 which has been maintained conductive by the output is rendered non-conductive. Therefore, the transistor 307 is turned off, i.e., the terminal b is electrically disconnected from the terminal c, so that the flow of field current to the field coil 1b is stopped. When, in contrast, the voltage at the terminal a is decreased, the transistor 307 is rendered conductive, so that the field current flows again. The above-described operation is repeatedly carried out, to regulate the output voltage of the generator 2. The pilot lamp 6 is turned on only when the voltage at the terminal a is lower than a predetermined value, and it is turned off when the generator is normally generating electricity, thus indicating the generation condition.
However, it is impossible for this display method to monitor whether or not the charging system comprising the generator, the full-wave rectifier, the voltage regulator, the battery, etc. is in an abnormal state. That is, the method cannot indicate, for instance, that the battery cannot be charged because it is electrically disconnected from the rectifier, that the generator is not working because the exciting circuit is out of order, that control is not suitably carried out, or that the diodes for charging the battery are defective. Likewise, this system cannot monitor the charging condition of the battery. When the charging system is out of order, this method cannot determine what the trouble is.